Cosmetically the white skin with little pigmentation, speckle, or freckle appears to be favored. For this reason a substance having a skin whitening effect and very safe even when used for an extended time is in demand. The pigmentation, spots, freckles, and the like, are generally considered to be caused as a result of the melanin production enhanced by the activated melanocyte present in the skin due to the stimulation from skin exposure to ultraviolet ray, hormonal imbalance, genetic factors, or the like. The mechanism of melanin production enhancement is complicated but it is known that melanin is biosynthesized by the enzyme tyrosinase activity and the dopa oxidase activity of tyrosinase is deeply involved with the melanin production mechanism (Non Patent Document 1). Skin whitening agents targeting this melanin production mechanism have been developed. For example, ascorbic acid, arbutin, kojic acid, and the like, have been reported as skin whitening agents having an effect for inhibiting the melanin production by inhibiting the enzyme tyrosinase activity (Non Patent Document 2).
Plant extracts having a skin whitening effect and inhibiting the dopa oxidase activity have been reported. Examples include toosendan (Melia toosendan Sieb. et Zucc.), souka (Amomum tsao-ka Crevost et Lemaire), seneshio gurashirisu (Senecio gracilis) and kokuriro (Veratrum nigrum L.) (Patent Document 1), garden angelica (Angelica archangelica), flowering dogwood (Benthamidia florida), kansui (Euphorbia kansui Liou), Japanese sumac (Rhus chinensis Mill.), okazeri (Cnidium monnieri (L.) Cuss.), hairvein agrimony (Agrimonia pilosa Ledeb.), rouro (Diuranthera minor (C. H. Wright) Hemsl.), and common barberry (Berberis aristata) (Patent Document 2), inukaramatsu (Pseudolarix amabilis), true indigo (Indigofera tinctoria) and devil's trumpet (Datura metel) (Patent Document 3), pomegranate (Punica granatum) flower (Patent Document 4), renshin (a bud of a Nelumbo nucifera Gaertn) (Patent Document 5), and Buddleja axillaris (Patent Document 6).
Kitsunenomago, Justicia procumbens, belonging to the Family Acanthaceae plant is known as shakujo in Kampo and is used for joint pains, fever, or the like. Justicia gendarussa (kidachikitsunenomago) also belonging to the same genus plant of the Family Acanthaceae is known as a preparation for external application to the skin analgesic or a preparation for external application to the skin antipruritic (Patent Document 7), and Thunbergia laurifolia, Rhinacanthus nasuta (L.) Kurz, and Andrographis paniculata, belonging to different genera plants of the same Family Acanthaceae are known to have the tyrosinase activity inhibitory effects, melanin production inhibitory effects, or skin whitening effects (Patent Documents 8 to 10).
However, it has not been known that the Family Acanthaceae, Genus Justicia, particularly Justicia procumbens, has the melanin production inhibitory effects and skin whitening effects.